Bra Size Calculator

Bra Size Calculator: Find Your Perfect Fit

A bra size calculator uses two simple body measurements to determine your band size and cup size. Wearing the wrong bra size is incredibly common, with studies suggesting up to 80% of women wear an ill-fitting bra. Our calculator takes the guesswork out of the process so you can shop with confidence.

How to Measure for Bra Size

You need two measurements. First, measure around your ribcage directly under your bust, keeping the tape snug and level. This is your band size. Second, measure around the fullest part of your bust, keeping the tape parallel to the floor. Subtract the band measurement from the bust measurement; each inch of difference represents one cup size. A 1-inch difference is an A cup, 2 inches is B, and so on.

Why Fit Matters

An ill-fitting bra can cause back pain, shoulder strain, skin irritation, and poor posture. Beyond comfort, the right bra provides proper support for breast tissue, reduces bounce during physical activity, and improves the silhouette of clothing. Your bra size can also change due to weight fluctuations, pregnancy, hormonal changes, or aging, so it is wise to remeasure periodically.

Sister Sizes and Variations

Sister sizing is the concept that you can go up a band size and down a cup size (or vice versa) and maintain similar cup volume. For example, 34C and 36B hold the same volume but on different band lengths. This is helpful when a particular size is out of stock or when a band feels too tight or too loose. Our calculator recommends your primary size and can suggest sister sizes as alternatives.

Frequently Asked Questions

How often should I measure my bra size?

Measure your bra size every 6 to 12 months. Weight changes of 5-10 pounds, pregnancy, breastfeeding, and hormonal shifts can all affect your size. Brands and styles also fit differently, so always try on before buying.

What if my band measurement is an odd number?

If your underbust measurement is an odd number, round up to the next even number for your band size. Bra bands are manufactured in even sizes (30, 32, 34, 36, etc.), so rounding ensures the tightest fit on the loosest hook.

What is the difference between US and UK bra sizes?

US and UK sizing differ after DD. US uses DDD (E) and DDDD (F/G), while UK uses E, F, FF, G, GG, H. Most international brands follow UK sizing for larger cup sizes. Check the brand's sizing chart before ordering.

What does a too-tight band or straps mean for fit?

If the band rides up in the back, the band is too loose. If the straps dig into your shoulders, the band is likely too loose and doing too much of the support work. About 80% of support should come from the band, not the straps.

Can I use this calculator for sports bra sizing?

Yes, but sports bras often use a simplified S/M/L sizing system or encapsulation sizing. For high-impact activities, choose a bra that encapsulates each breast individually and uses a racerback or compression design for maximum support.

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